Curable silicone compositions are used for the resin-sealing of optical semiconductor elements, for example, photocouplers, light-emitting diodes, solid-state imaging devices, and so forth. Silicone cured product obtained from such a curable silicone composition must not absorb or scatter the light emitted from the optical semiconductor element or the light incident on the element, and, in order to improve the reliability of the resin-sealed optical semiconductor element, this cured product must also not discolor or undergo a decline in adhesiveness.
For example, Japanese Unexamined Patent Application Publication (hereinafter referred to as “Kokai”) 2009-185226 provides a thermosetting silicone composition comprising: (A) an organopolysiloxane represented by the average compositional formula: R1n(C6H5)mSiO(4−n−m)/2, wherein each R1 is independently a hydroxyl group, an alkoxy group, or a substituted or unsubstituted monovalent hydrocarbon group excluding unsubstituted phenyl, 30 to 90 mole % of all groups designated by R1 are alkenyl groups; and n and m are positive numbers that satisfy: 0.1≦n<0.8, 0.2≦m<1.9, 1≦n+m<2, and 0.20≦m/(n+m)≦0.95; (B) an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms in one molecule and represented by the average compositional formula: R2aHbSiO(4−a−b)/2, wherein each R2 is independently a substituted or unsubstituted monovalent hydrocarbon group excluding aliphatically unsaturated hydrocarbon groups and excluding substitution by an epoxy group and excluding substitution by an alkoxy group; and a and b are positive numbers that satisfy: 0.75≦a≦2.1, 0.01≦b≦1.0, and 0.8≦a+b≦3.0, in a quantity that provides a value of 0.5 to 4.0 for the molar ratio of the total amount of silicon-bonded hydrogen atoms in the composition to all silicon-bonded alkenyl groups in the composition; and (C) a hydrosilylation reaction catalyst. In addition, when this composition is subjected to measurement using a curastometer, the time to reach a torque of 1 dNm at the molding temperature from immediately after the start of the measurement is at least 5 seconds and the time to reach a torque of 20 dNm from a torque of 1 dNm at the molding temperature is not more than 2 minutes. This composition has a high hot strength at the molding temperature and can be used, for example, for injection molding; however, it undergoes a major decline in viscosity at elevated temperatures, which causes the problem of a high defect rate during transfer molding or compression molding due to the appearance of flashing and the inclusion of voids.
Kokai 2006-213789, on the other hand, provides a curable silicone composition comprising: (A) an organopolysiloxane that has on average at least 0.2 silicon-bonded alkenyl groups in one molecule; (B) an organopolysiloxane that has a three-dimensional network structure, is represented by the average unit formula: (R′3SiO1/2)a (SiO4/2)b, wherein each R′ is independently a substituted or unsubstituted monovalent hydrocarbon group, a and b are each positive numbers, and a/b is a number from 0.2 to 3, and contains from 400 to 5,000 ppm of silicon-bonded hydroxyl groups, at 10 to 80 weight % with reference to the total amount of components (A) and (B); (C) an organohydrogenpolysiloxane that has at least two silicon-bonded hydrogen atoms in one molecule, in a quantity that provides from 0.2 to 5 moles of silicon-bonded hydrogen atoms in this component per 1 mole of the total of the silicon-bonded alkenyl groups in component (A) and the silicon-bonded alkenyl groups in component (B); and (D) a catalytic quantity of a hydrosilylation reaction catalyst.
Kokai 2006-299099 provides a resin composition for sealing an optical semiconductor element, in the form of an addition-curable silicone resin composition in which the essential components are (A) an organosilicon compound that has in one molecule at least two noncovalent bonding double bond groups and that contains at least 30 to 100 mass %, with reference to component (A) as a whole, of an organopolysiloxane represented by the average compositional formula: (R1SiO3/2)a(R2R3SiO)b(R4R5R6SiO1/2)c(SiO4/2)d, wherein R1 to R6 each independently represent a monovalent hydrocarbon group, from 1 to 50 mole % of all monovalent hydrocarbon groups are groups containing a noncovalent bonding double bond; and a, b, c, and d are positive numbers that represent the molar ratios of the individual siloxane units wherein a/(a+b+c+d)=0.40 to 0.95, b/(a+b+c+d)=0.05 to 0.60, c/(a+b+c+d)=0 to 0.05, d/(a+b+c+d)=0 to 0.10, and a+b+c+d=1.0; (B) an organohydrogenpolysiloxane that has at least two silicon-bonded hydrogen atoms in one molecule; and (C) a platinum-type catalyst in a catalytic amount, wherein the organopolysiloxanes of components (A) and (B) do not contain the silanol group.
These compositions are known to exhibit a smaller decline in viscosity at elevated temperatures than curable silicone compositions that contain a high phenyl group concentration; however, when the branched polymer content is raised in order to obtain a hardness high enough to provide a satisfactory mechanical strength and a low surface tack, a large viscosity decline occurs and the viscosity declines at elevated temperatures just as for the curable silicone compositions that contain a high phenyl group concentration. The same problems as described above then occur in transfer molding and compression molding.
An object of the present invention is to provide a curable silicone composition for sealing an optical semiconductor element wherein the composition can efficiently perform resin sealing by transfer molding or compression molding while exhibiting an excellent moldability and can provide a cured product that has a low surface tack.
A further object of the present invention is to provide a method that efficiently carries out the resin sealing of an optical semiconductor element using this composition and that does so while exhibiting an excellent moldability.
Another object of the present invention is to provide an optical semiconductor element that is obtained by this method and that exhibits a low surface tack, little flashing, and few voids.